There's a few variables to consider.
Which would you miss more, 9000 avios or the 150 odd quid? BA will currently sell you 9000 avios for a shade under 150 quid.
I did this flight last year and an extra 1000 yen at booking got my partner and myself a seat in J Class which is good for 40TPs. It may be worth throwing that into the mix if you're in the need of the TPs. It will however earn you very few actual avios.
On the flight we were on at least, a window seat on the left hand side made for a nice view of Fujisan during the flight.
My membership year ends on 8 May, I currently have 290 TP and 100 TP worth of flights in the next two weeks. So an extra 40 TP in April won't do me any good :-(